JP2007170888A - Optical element testing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection device capable of determining acceptability of an optical element under inspection by detecting with once measurement of surface shape error, eccentric error between surfaces, refractive index distribution etc. , even without reference lens. <P>SOLUTION: The optical element inspection device comprises: a light source 11; a light flux splitting means 18 for splitting the light flux from the light source 11 into light flux M to be inspected and reference light flux R; a correction optical system 23 arranged in a light flux M to be inspected in which an optical element 22 under inspection is arranged for converting the transmission wave front of the optical element 22 under inspection based on the design value; a light flux composition means 26 for compositing the light flux M to be inspected transmitted through the correction optical system 23 and reference light flux R collimated via different light path from the light flux M to be inspected; an imaging means 28 for imaging the light flux transmitted through the light flux composition means 26; a parameter calculation means 31 for calculating the parameter regarding the wave front transmitted through the detection optical element 22 based on the interference fringe formed by the imaging means 28; and an evaluation value operation means 31 for calculating the evaluation value of the optical element 22 under inspection based on the parameters. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical element inspection apparatus, and more particularly, to an apparatus for inspecting an optical element by measuring interference fringes on a transmission wavefront of the optical element, and in particular, a surface shape, a surface interval, and a surface-to-surface distance of the optical element. The present invention relates to an inspection apparatus capable of determining pass / fail of an optical element by measuring decentration, refractive index distribution and the like at a time.

Conventionally, as a comprehensive inspection method for optical elements, for example, there is a comprehensive lens inspection machine disclosed in Patent Document 1. This inspection machine divides a light beam from a light source into two parts, a test lens and a reference lens are arranged in the two optical paths, and a wavefront aberration generated in the optical path of the test lens and a wavefront generated in the optical path of the reference lens By analyzing the interference fringes obtained as the difference in aberration, the values of the lens surface shape, lens thickness, decentration, etc. are known. As a reference lens, find a lens close to the design value of the test lens from several test lenses, or create a lens with high accuracy close to the design value by grinding or the like and use it as the reference lens It is.
Japanese Patent No. 3206984

  However, when the lens to be tested is a plastic optical element, it is very difficult to manufacture a reference lens for the following reason, so that the inspection cannot be performed by the conventional technique. In other words, the optical characteristics of plastic optical elements change over time due to moisture absorption, etc., and the optical surface of the lens is easily scratched. Cannot be used as a reference lens. In addition, plastic optical elements have a high degree of freedom in molding due to their material characteristics, and are often optical elements having a more complicated shape than glass optical elements. Therefore, it is very difficult to manufacture a reference lens equivalent to plastic with glass.

  The present invention has been made by paying attention to such problems of the prior art, and its purpose is to reduce the surface shape error, inter-surface decentration error, refractive index distribution, etc. of the optical element to be tested without a reference lens. An object of the present invention is to provide an inspection apparatus that can detect a single measurement and determine whether the optical element to be detected is acceptable or not.

  In order to solve the above problems, a first optical element inspection apparatus of the present invention includes a light source, a light beam splitting unit that splits a light beam from the light source into a test light beam and a reference light beam, and a test optical element. A correction optical system that is arranged in the test light beam and converts the transmitted wavefront of the test optical element based on a design value into a substantially flat surface, and a test light beam that passes through the correction optical system and the optical path different from the test light beam A light beam synthesizing unit that synthesizes the reference light beam that has been converted into a parallel light beam, an imaging unit that images the light beam that has passed through the light beam synthesizing unit, and the optical to be tested based on interference fringes formed by the imaging unit Parameter calculating means for calculating a parameter relating to a wavefront transmitted through the element, and evaluation value calculating means for calculating an evaluation value of the optical element to be tested based on the parameter are provided.

  According to this configuration, the wavefront on which the error component transmitted through the test optical element is mounted becomes a substantially plane wave including an error by the correction optical system that converts the transmitted wavefront of the test optical element based on the design value into a substantially plane. Since it is converted, the transmitted wavefront of the test optical element can be measured without using a reference lens, and it is possible to determine whether the test optical element is acceptable. It is particularly suitable when the optical element to be tested is a plastic optical element.

  The second optical element inspection apparatus of the present invention includes a light source, a light beam dividing means for dividing the light beam from the light source into a test light beam and a reference light beam, at least one reflecting means for deflecting the test light beam, A correction optical system that is disposed in a test light beam in which an optical element is disposed and converts a transmitted wavefront of the test optical element based on a design value into a substantially flat surface; a test light beam that has passed through the correction optical system; From a light beam combining means for combining the reference light beam that has been converted into a parallel light beam through an optical path different from the inspection light beam, an image pickup means for picking up the light beam that has passed through the light beam combining means, and an interference fringe formed by the image pickup means An optical element inspection apparatus comprising a calculation means for determining whether or not the test optical element is acceptable, wherein at least one of the reflection means for deflecting the test light beam is a reflection surface of the test optical element. Is what .

  According to this configuration, since the test light beam is deflected by the reflection surface of the test optical element, the transmitted wavefront of the prism type test optical element including at least one reflection surface can be easily measured. It is possible to determine whether the optical analysis element is acceptable or not.

  According to a third optical element inspection apparatus of the present invention, in the first and second optical element inspection apparatuses, the correction optical system has at least one rotationally symmetric optical surface and at least one rotationally asymmetric optical surface. It is characterized by that.

  According to this configuration, even when the wavefront transmitted through the test optical element has a rotationally asymmetric shape, it is possible to form an interference fringe that can be analyzed by converting the transmitted wavefront into a substantially plane wave by the correction optical system, It is possible to determine whether or not the optical element is acceptable.

  According to a fourth optical element inspection apparatus of the present invention, in the first optical element inspection apparatus, the evaluation value calculating means calculates the transmitted wavefront of the optical element to be calculated using the design value of the optical element to be detected. The evaluation value of the optical element to be measured is calculated by comparing the parameter according to the above and the parameter from the parameter calculation means.

  According to this configuration, since the transmitted wavefront serving as a reference is obtained by calculation, it is not necessary to prepare a master sample (such as a reference lens) having no manufacturing error. Can be done.

  As is clear from the above description, according to the optical element inspection apparatus of the present invention, even if there is no reference lens, the surface shape error, inter-surface decentration error, refractive index distribution, etc. of the optical element to be detected can be detected by one measurement. The pass / fail of the test optical element can be determined. In particular, when the optical element to be tested is a plastic optical element, the pass / fail judgment can be easily performed by using the optical inspection apparatus of the present invention.

  Below, the optical element inspection apparatus of this invention is demonstrated based on an Example.

  FIG. 1 is a diagram showing a configuration of an optical element inspection apparatus according to Embodiment 1 of the present invention. The optical element inspection apparatus 51 measures the transmission wavefront of the optical element to be detected as an interference fringe using a Mach-Zehnder interferometer, analyzes the interference fringe, fits the digitized transmission wavefront to a Zernike polynomial, and then uses the Zernike polynomial. It is the inspection apparatus which determines the pass / fail of the optical element to be tested using the coefficient.

  In FIG. 1, the light beam from the laser light source 11 passes through the variable ND filter 12 and the polarizing plate 13, and then the wavefront noise is removed by the spatial filter 16 including the objective lens 14 and the pinhole 15. It becomes a spherical wave. The light beam that has passed through the spatial filter 16 becomes parallel light by the collimator lens 17 and is divided into transmitted light and reflected light by the light beam dividing means 18. This transmitted light and reflected light correspond to the reference light beam R and the test light beam M, respectively.

  The reference light beam R is expanded to an appropriate light beam diameter by the beam expander 19, reflected by the reference light beam reflecting member 20, and enters the light beam combining unit 26. On the other hand, the test light beam M is reflected by the test light beam reflecting member 21, passes through the test optical element 22, is composed of two spherical lenses 24 and 25, and is formed of the test optical element 22 based on the design value. By passing through the correction optical system 23 that converts the transmitted wavefront into a substantially plane, the wavefront deformed by the optical element 22 to be tested is converted into a substantially plane wave including an error, and enters the light beam combining means 26. Then, the reference light beam R and the test light beam M are superimposed by the light beam combining unit 26 to generate interference fringes.

  As described above, since the optical element inspection apparatus 51 of the present invention measures the transmitted wavefront of the optical element 22 to be measured, the surface shape, the surface interval, the inter-surface eccentricity, the absolute refractive index, the refraction of the optical element 22 to be measured All items constituting the optical element 22 such as a rate distribution can be inspected. Therefore, the optical element inspection apparatus 51 of the present invention is suitable for pass / fail determination for determining whether the manufactured optical element 22 is a good product or a defective product.

  In the present embodiment, the test optical element 22 is constituted by a rotationally symmetric optical surface. In that case, the correction optical system 23 for converting the wavefront into a substantially plane is also composed of rotationally symmetric optical elements. In this embodiment, the correction optical system 23 is composed of two spherical lenses 24 and 25, but may of course be composed of lenses including a flat surface, an aspherical surface and the like. Of course, there is no limit on the number of lenses.

  The interference light beam that has passed through the light beam combining unit 26 is defined by the field stop 27 and then enters the image pickup unit 28 including the zoom lens 29 and the CCD 30, and is taken into the interference fringe analyzer 31 as image information. Interference fringe analysis is performed. Interference fringe analysis is performed by a fringe scan method. The reference light beam reflecting member 20 is moved in the direction perpendicular to the reflecting surface by the piezoelectric element, and the optical path difference between the test light beam M and the reference light beam R is changed. A plurality of interference fringes with different optical path differences are taken into the interference fringe analyzer (PC) 31 as image information, and the phase data W (ρ, θ) of the interference wavefront is digitized by arithmetic processing. 1 is an input device to the interference fringe analyzer (PC) 31, and reference numeral 33 is an output device from which the result of the interference fringe analyzer (PC) 31 is output.

  The digitized phase data W (ρ, θ) of the interference wavefront is fitted to a Zernike polynomial (formula (1) of Patent Document 1), and the coefficient of the Zernike polynomial is output to the output device 33 as an analysis result. The pass / fail of the test optical element is determined by the coefficient of the Zernike polynomial. Details will be described later.

  Note that the wavefront emitted from the optical element 22 to be measured is generally a wavefront greatly deviated from the plane wave. Therefore, when the interference fringe between the wavefront and the reference plane wave is measured, the interference fringe density becomes too high, and the interference fringe analysis is performed. Although it becomes impossible, the correction optical system 23 converts the outgoing wavefront from the optical element 22 to be tested into a substantially plane wave, so that the density of the interference fringes is lowered and the interference fringe analysis device 31 can perform the interference fringe analysis.

  The light beam combining means 26 is held by a stage capable of biaxial tilt adjustment. Depending on the installation position of the optical element 22 to be detected, a large tilt component may be added to the generated interference fringe. However, the tilt component included in the interference fringe is removed by the biaxial tilt adjustment of the light beam combining unit 26. Can do.

  The optical element inspection apparatus 51 measures the transmitted wavefront of the optical element 22 to be measured by a Mach-Zehnder interferometer. By adopting such a configuration, since the number of times the light beam passes through the test optical element 22 is only one, the measurement sensitivity does not increase excessively. Therefore, the allowable position error when the test optical element 22 is installed. Can be increased. It is also possible to achieve both a dynamic range and a measurement region while maintaining appropriate measurement sensitivity. Since all the embodiments of the present invention have the configuration of a Mach-Zehnder interferometer, the above-described effects can be obtained in all the embodiments.

  FIG. 2 is a flowchart showing the pass / fail determination procedure of the optical element 22 to be tested. As shown in the upper line of FIG. 2, first, the interference wavefront of the optical element 22 to be measured is measured, and the coefficient of the Zernike polynomial is derived by interference fringe analysis. Separately, as shown in the lower line of FIG. 2, the interference fringes are simulated using the design values (surface shape, surface interval, refractive index, etc.) of the test object, and similarly, the coefficients of the Zernike polynomial are used. Is derived. Then, as shown in the center line of FIG. 2, the coefficients of both Zernike polynomials are compared with each other, and it is determined whether or not the difference between both is larger than a preset threshold value. I do. It should be noted that which term of the Zernike polynomial is used for pass / fail determination is appropriately determined according to the optical characteristics of the optical element 22 to be measured and the manufacturing process.

  As described above, since the optical element inspection apparatus 51 according to the first embodiment can perform pass / fail determination of the optical element 22 to be tested without using the reference lens, it is difficult to manufacture the reference lens. It is suitable for pass / fail judgment.

  Next, an optical element inspection apparatus according to Example 2 of the present invention will be described. FIG. 3 is a diagram showing the configuration of the optical element inspection apparatus according to Embodiment 2 of the present invention. The basic configuration is the same as that of the optical element inspection apparatus according to the first embodiment shown in FIG. 1, but the configuration of the test optical path is different because the test optical element 34 is different.

  That is, the test optical element 34 includes three optical surfaces (A surface, B surface, and C surface), and each optical surface has a free-form surface shape. When the parallel light from the laser is incident on the optical surface of the optical element to be tested 34, the wavefront emitted from another optical surface has a shape greatly deviated from the plane, so that the interference fringe density increases and the interference fringe analysis is performed. Although it cannot be performed, interference fringe analysis can be performed by performing wavefront conversion, that is, conversion to a substantially plane wave, by the correction optical system 35 having the same function as the correction optical system 23 of the first embodiment.

  The free-form surface in the present invention is defined by the following formula (a).

∞
Z = cr ² / [1 + √ {1− (1 + k) c ² r ² }] + ΣC _j X ^m Y ^{n
j = 2}
... (a)
Here, the first term of the equation (a) is a spherical term, and the second term is a free-form surface term.

In the spherical term, the meanings of c, k, and r are as follows.
c: curvature of vertex k: conic constant (conical constant)
r = √ (X ² + Y ² )
Moreover, when the free-form surface term is expanded, it is expressed as follows.

∞
ΣC _j X ^m Y ^{n
j = 2}
= C ₂ X + C ₃ Y
+ C ₄ X ² + C ₅ XY + C ₆ Y ²
+ C ₇ X ³ + C ₈ X ² Y + C ₉ XY ² + C ₁₀ Y ³
+ C ₁₁ X ⁴ + C ₁₂ X ³ Y + C ₁₃ X ² Y ² + C ₁₄ XY ³ + C ₁₅ Y ⁴
+ C ₁₆ X ⁵ + C ₁₇ X ⁴ Y + C ₁₈ X ³ Y ² + C ₁₉ X ² Y ³ + C ₂₀ XY ⁴
+ C ₂₁ Y ⁵
+ C ₂₂ X ⁶ + C ₂₃ X ⁵ Y + C ₂₄ X ⁴ Y ² + C ₂₅ X ³ Y ³ + C ₂₆ X ² Y ⁴
+ C ₂₇ XY ⁵ + C ₂₈ Y ⁶
+ C ₂₉ X ⁷ + C ₃₀ X ⁶ Y + C ₃₁ X ⁵ Y ² + C ₃₂ X ⁴ Y ³ + C ₃₃ X ³ Y ⁴
+ C ₃₄ X ² Y ⁵ + C ₃₅ XY ⁶ + C ₃₆ Y ⁷
・ ・ ・ ・ ・ ・
However, C _j (j is an integer of 2 or more) is a coefficient.

  FIG. 4 shows how light beams pass through the imaging optical system 48 using the optical element 34 to be tested. A chief ray and a marginal ray at an angle of view of 0 ° are shown. The imaging optical system 48 includes a test optical element 34 (test optical element of Example 2), a test optical element 40 (test optical element of Example 3), and cover glasses 45 and 46. Reference numeral 47 denotes an imaging surface of the imaging optical system 48.

  Table 1 shows numerical data of optical members constituting the imaging optical system 48. In the configuration parameters of this embodiment, the axial principal ray is defined as a ray that passes from the center of the object vertically through the center of the stop of the optical system to the center of the image plane. Then, the position intersecting the axial principal ray of the first surface closest to the object side of the optical system (in the case of FIG. 4, the surface on the object side of the cover glass 45) is defined as the origin of the decentered optical surface of the decentered optical system. The direction along the upper principal ray is the Z-axis direction, the direction from the object toward the first surface is the Z-axis positive direction, the plane on which the optical axis is bent is the YZ plane, passes through the origin, and is orthogonal to the YZ plane. The direction is the X-axis direction, the direction from the front to the back of FIG. 4 is the X-axis positive direction, and the X-axis, the Z-axis, and the axis constituting the right-handed orthogonal coordinate system are the Y-axis.

  For the decentered surface, the amount of decentering from the center of the origin of the optical system to the surface top position of the surface (X, Y, and Z directions are X, Y, and Z, respectively) and X of the center axis of the surface Tilt angles (α, β, γ (°), respectively) about the axis, the Y axis, and the Z axis are given. In this case, positive α and β mean counterclockwise rotation with respect to the positive direction of each axis, and positive γ means clockwise rotation with respect to the positive direction of the Z axis. Note that the α, β, and γ rotations of the central axis of the surface are performed by first rotating the central axis of the surface and its XYZ orthogonal coordinate system by α counterclockwise around the X axis, and then rotating the rotation. The center axis of the surface is rotated β counterclockwise around the Y axis of the new coordinate system, and the coordinate system rotated once is also rotated β counterclockwise around the Y axis and then rotated twice. The center axis of the surface is rotated γ clockwise around the Z axis of the new coordinate system.

  In addition, a surface interval is given when a specific surface and subsequent surfaces among the optical action surfaces constituting the optical system of each embodiment constitute a coaxial optical system. In the numerical data, “FFS” indicates a free-form surface, and “REF” indicates a reflective surface. The refractive index and Abbe number are those of the d line.

[Table 1]
Surface number Curvature radius Surface spacing Eccentricity Refractive index Abbe number Object surface ∞ ∞
1 ∞ Eccentricity (1) 1.4950 65.0
2 ∞ Eccentricity (2)
3 FFS [1] Eccentricity (3) 1.6069 27.0
4 FFS [2] Eccentricity (4) 1.6069 27.0
5 FFS [3] Eccentricity (5)
6 ∞ (diaphragm surface) Eccentricity (6)
7 FFS [4] Eccentricity (7) 1.5256 56.4
8 FFS [5] Eccentricity (8) 1.5256 56.4
9 FFS [6] Eccentricity (9) 1.5256 56.4
10 FFS [7] 0.31 Eccentricity (10)
11 ∞ 0.30 1.5163 64.1
12 ∞ 0.63
Image plane ∞
FFS [1]
C ₄ = 4.1709 × 10 ^-2 C ₆ = 6.5908 × 10 ^-2 C ₈ = -1.0688 × 10 ^-4
C ₁₀ = -1.1246 × 10 ^-3 C ₁₁ = 6.6599 × 10 ^-4 C ₁₃ = 1.6298 × 10 ^-3
C ₁₅ = 7.4708 × 10 ^-4 C ₁₇ = -2.9507 × 10 ^-5 C ₁₉ = 9.7169 × 10 ^-5
C ₂₁ = -1.7566 × 10 ^-4 C ₂₂ = -2.5840 × 10 ^-6 C ₂₄ = 5.7315 × 10 ^-5
C ₂₆ = -3.4271 × 10 ^-5 C ₂₈ = 3.0860 × 10 ^-5
FFS [2]
C ₄ = -3.9587 × 10 ^-3 C ₆ = 2.7654 × 10 ^-2 C ₈ = -1.0723 × 10 ^-3
C ₁₀ = 1.9555 × 10 ^-3 C ₁₁ = 7.7516 × 10 ^-5 C ₁₃ = -1.7029 × 10 ^-4
C ₁₅ = 3.4007 × 10 ^-4 C ₁₇ = -3.4680 × 10 ^-5 C ₁₉ = 1.0476 × 10 ^-4
C ₂₁ = 4.8180 × 10 ^-6 C ₂₂ = -6.2801 × 10 ^-6 C ₂₄ = -4.7571 × 10 ^-7
C ₂₆ = 1.6082 × 10 ^-5 C ₂₈ = -8.1118 × 10 ^-6
FFS [3]
C ₃ = -3.3425 × 10 ^-2 C ₄ = -7.8403 × 10 ^-2 C ₆ = -4.0695 × 10 ^-2
C ₈ = -8.8984 × 10 ^-3 C ₁₀ = 6.2496 × 10 ^-3 C ₁₁ = -1.5720 × 10 ^-3
C ₁₃ = -2.7166 × 10 ^-2 C ₁₅ = 1.4357 × 10 ^-3 C ₁₇ = -6.5515 × 10 ^-4
C ₁₉ = 3.6911 × 10 ^-4 C ₂₁ = -2.1928 × 10 ^-4 C ₂₂ = 1.8341 × 10 ^-3
C ₂₄ = -3.0393 × 10 ^-3 C ₂₆ = 2.0951 × 10 ^-3 C ₂₈ = -6.7649 × 10 ^-4
FFS [4]
C ₃ = -2.8391 × 10 ^-2 C ₄ = 1.2123 × 10 ^-1 C ₆ = -8.3113 × 10 ^-2
C ₈ = 7.8309 × 10 ^-3 C ₁₀ = 2.1910 × 10 ^-3 C ₁₁ = 6.5905 × 10 ^-3
C ₁₃ = -1.7892 × 10 ^-2 C ₁₅ = 1.5127 × 10 ^-3 C ₁₇ = -6.7547 × 10 ^-4
C ₁₉ = 4.3224 × 10 ^-4 C ₂₁ = -8.3463 × 10 ^-5 C ₂₂ = -2.3991 × 10 ^-4
C ₂₄ = -8.1334 × 10 ^-3 C ₂₆ = 7.9144 × 10 ^-4 C ₂₈ = -4.9662 × 10 ^-4
FFS [5]
C ₄ = 3.8550 × 10 ^-2 C ₆ = 4.1924 × 10 ^-2 C ₈ = 1.7538 × 10 ^-3
C ₁₀ = -3.9045 × 10 ^-4 C ₁₁ = 8.7475 × 10 ^-5 C ₁₃ = 6.4778 × 10 ^-4
C ₁₅ = 1.7386 × 10 ^-4 C ₁₇ = -1.0376 × 10 ^-5 C ₁₉ = -1.6202 × 10 ^-6
C ₂₁ = -1.7314 × 10 ^-5 C ₂₂ = -2.3351 × 10 ^-7 C ₂₄ = 1.1257 × 10 ^-5
C ₂₆ = -9.6773 × 10 ^-6 C ₂₈ = -9.8518 × 10 ^-6
FFS [6]
C ₄ = -2.4098 × 10 ^-2 C ₆ = 1.1095 × 10 ^-2 C ₈ = 2.5243 × 10 ^-4
C ₁₀ = 8.0683 × 10 ^-5 C ₁₁ = -1.0086 × 10 ^-4 C ₁₃ = 8.3763 × 10 ^-4
C ₁₅ = 3.5919 × 10 ^-4 C ₁₇ = -6.6515 × 10 ^-5 C ₁₉ = 5.2149 × 10 ^-5
C ₂₁ = 6.6212 × 10 ^-5 C ₂₂ = 4.1040 × 10 ^-7 C ₂₄ = 4.0895 × 10 ^-6
C ₂₆ = -6.4842 × 10 ^-6 C ₂₈ = -9.8152 × 10 ^-6
FFS [7]
C ₃ = 4.8640 × 10 ^-2 C ₄ = 3.7051 × 10 ^-2 C ₆ = 6.3083 × 10 ^-2
C ₈ = 1.4429 × 10 ^-3 C ₁₀ = 2.1610 × 10 ^-4 C ₁₁ = -8.4235 × 10 ^-3
C ₁₃ = -8.8574 × 10 ^-3 C ₁₅ = -4.6112 × 10 ^-3 C ₁₇ = -4.4861 × 10 ^-4
C ₁₉ = 5.3081 × 10 ^-4 C ₂₁ = 1.1103 × 10 ^-3 C ₂₂ = 4.3529 × 10 ^-4
C ₂₄ = 5.0879 × 10 ^-4 C ₂₆ = 1.0880 × 10 ^-3 C ₂₈ = -1.2467 × 10 ^-4
Eccentricity (1)
X = 0.00 Y = 0.00 Z = 0.00
α = 0.00 β 0.00 γ = 0.00
Eccentricity (2)
X = 0.00 Y = 0.00 Z = 0.50
α = 0.00 β = 0.00 γ = 0.00
Eccentricity (3)
X = 0.00 Y = -0.00 Z = 0.64
α = -0.95 β = 0.00 γ = 0.00
Eccentricity (4)
X = 0.00 Y = -0.02 Z = 3.34
α = -41.75 β = 0.00 γ = 0.00
Eccentricity (5)
X = 0.00 Y = 2.63 Z = 3.02
α = -83.86 β = 0.00 γ = 0.00
Eccentricity (6)
X = 0.00 Y = 3.21 Z = 2.96
α = -83.86 β = 0.00 γ = 0.00
Eccentricity (7)
X = 0.00 Y = 3.39 Z = 2.94
α = -83.86 β = 0.00 γ = 0.00
Eccentricity (8)
X = 0.00 Y = 7.89 Z = 2.41
α = -101.29 β = 0.00 γ = 0.00
Eccentric (9)
X = 0.00 Y = 5.44 Z = 1.03
α = -150.09 β = 0.00 γ = 0.00
Eccentricity (10)
X = 0.00 Y = 5.38 Z = 4.48
α = -180.00 β = 0.00 γ = 0.00
.

  In the actual use state shown in FIG. 4, the test optical element 34 constituting the imaging optical system 48 refracts the light beam incident on the A surface, reflects the light beam on the B surface, and refracts the light beam on the C surface. Then, a light beam is emitted from the optical element 34 to be tested from the C plane. In order to approximate such a light beam passing state, the optical element inspection apparatus shown in FIG. 3 deflects the test light beam on the reflection surface (B surface) of the test optical element 34.

  By adopting such a configuration, since the light beam close to the actual use state passes through the test optical element 34, the transmitted wavefront of the test optical element 34 measured by the optical element inspection apparatus 51 and the imaging optical system 48 Optical performance can be associated with each other, and it is possible to make a pass / fail determination that is highly correlated with actual optical performance. In all of the embodiments of the present invention, since the light beam close to the actual use state passes through the test optical element, the above-described effects can be obtained in all the embodiments.

  In the optical element inspection apparatus 51 shown in FIG. 3, the light beam is incident on the C surface of the optical element 34 to be tested, the light beam is reflected on the B surface, and the light beam is emitted from the A surface. This configuration is derived from the ease of installation of the test optical element 34 in the optical element inspection apparatus 51. Of course, the light beam is incident on the A surface of the test optical element 34, and the light beam is reflected by the B surface. The light beam may be emitted from the C plane.

  FIG. 5 is a diagram showing a configuration of the correction optical system 35 incorporated in the optical element inspection apparatus 51 of FIG. The correction optical system 35 includes a cemented spherical lens 36 and a cylindrical surface lens 37. Since the outgoing wavefront from the test optical element 34 has a rotationally asymmetric shape, the correction optical system 35 includes an optical element 37 having a rotationally asymmetric optical surface. By arranging such a correction optical system 35 behind the test optical element 34, the wavefront emitted from the test optical element 34 can be converted into a substantially plane wave, and the fringe density of interference fringes observed by the CCD 30 is obtained. Becomes low and becomes an interference fringe that can be analyzed.

  FIG. 6 is a diagram illustrating an example of a simulation result of interference fringes generated when the test optical element 34 and the correction optical system 35 are incorporated in the optical element inspection apparatus 51. Thus, by converting the outgoing wavefront from the test optical element 34 into a substantially plane wave by the correction optical system 35, an interference fringe having a low fringe density and analyzable is generated. Note that the pass / fail judgment method of the optical element 34 to be tested is the same as in the first embodiment.

  Even when there is no manufacturing error in the test optical element 34, the wavefront converted by the correction optical system 35 does not coincide with the wavefront of the reference light beam. That is, the transmitted wavefront of the optical element 34 to be used as a criterion for pass / fail judgment is not a plane wave but a wavefront shape including a certain distortion. By performing the pass / fail determination of the test optical element 34 in this way, it is not necessary to convert the outgoing wavefront from the correction optical system 35 into a complete plane wave. Therefore, the design freedom of the correction optical system 35 is increased, and the structure Thus, the correction optical system 35 can be easily manufactured. Moreover, even if the optical element has a complicated shape, it is possible to easily perform pass / fail determination.

  FIG. 7 shows an enlarged view of the test optical element 34 in FIG. 5 and its periphery. Hereinafter, the installation position of the test optical element 34 in the optical element inspection apparatus 51 will be described with reference to FIG. The test optical element 34 is installed so that the optical axis of the light beam incident on the test optical element 34 coincides with the central axis of the surface corresponding to the diaphragm surface of the imaging optical system (the p surface in FIG. 7). Furthermore, the optical axis of the light beam emitted from the test optical element 34 coincides with the central axis of the surface (q surface in FIG. 7) corresponding to the object side surface of the cover glass 45 of the imaging optical system 48 (FIG. 4). Thus, the optical element 34 to be tested is installed. By installing the test optical element 34 in this way, the central axis of the correction optical system 35 arranged as numerical data described later is made to coincide with the optical axis of the light beam emitted from the test optical element 34. The interference fringes as shown in FIG. 6 can be generated.

  Table 2 below shows numerical data of optical members constituting the correction optical system 35 shown in FIG. The test optical element 34 in FIG. 5 is equivalent to the test optical element 34 included in the imaging optical system 48 in FIG. 4, but the direction of the light beam is opposite. That is, in the test optical element 34 in FIG. 4, the light beam passes in the order of the A plane, the B plane, the C plane, and the aperture plane, but in the test optical element 34 in FIG. 5, the aperture plane, the C plane, the B plane, Passes in order of A side.

  In the numerical data in Table 2, “CYL” indicates a cylindrical optical surface. The cylindrical optical surface is an optical surface having a different curvature radius in the Y direction and a curvature radius in the X direction. Numerical data is shown with the respective curvature radii being “RDY” and “RDX”. In the following numerical data, the optical surface of the optical element 34 to be tested is omitted. The optical surface of the test optical element 34 is described in the numerical data of the imaging optical system 48 in Table 1 above. The a-plane to e-plane correspond to the optical surface of the correction optical system 35 shown in FIG. 5, and the q-plane corresponds to the object-side surface of the cover glass 45 shown in FIG.

[Table 2]
Surface number Curvature radius Surface spacing Refractive index (d-line) Abbe number (d-line)
1 (q-plane) ∞ 17.80
2 (a side) 131.65 2.50 1.7283 28.5
3 (B side) 16.49 11.00 1.6667 48.3
4 (c surface) -24.47 208.22
5 (d surface) CYL [1] 8.00 1.5163 64.1
6 (e surface) CYL [2]
RDY RDX
CYL [1] ∞ 519.00
CYL [2] ∞ -103.80.

  Next, an optical element inspection apparatus according to Embodiment 3 of the present invention will be described. FIG. 8 is a diagram showing the configuration of the optical element inspection apparatus according to Embodiment 3 of the present invention. The basic configuration is the same as that of the optical element inspection apparatus according to the first embodiment shown in FIG. 1, but the configuration of the test optical path is different because the test optical element 40 is different.

  That is, the test optical element 40 includes four optical surfaces (D surface, E surface, F surface, and G surface), and each optical surface has a free-form surface shape. As in the second embodiment, the wavefront emitted from the test optical element 40 has a shape greatly deviating from the flat surface, so that the interference fringe density increases and interference fringe analysis cannot be performed. Interference fringe analysis can be performed by performing wavefront conversion, that is, conversion to a substantially plane wave, by the correction optical system 41 having the same function as the correction optical system 23.

  In the actual use state as shown in FIG. 4, the test optical element 40 constituting the imaging optical system 48 is refracted by diverging light incident on the D surface, the light beam is reflected on the E surface and the F surface, and the G surface. Then, the light beam is refracted, and the light beam is emitted from the G optical element 40 through the G plane. In the optical element inspection apparatus shown in FIG. 8, in order to approximate such a light beam passage state, the test light beam is deflected on the reflection surface (E surface and F surface) of the test optical element 40, and The diverging light is incident on the D surface of the test optical element 40 by disposing the condenser lens 39 in front of the test optical element 40.

  FIG. 9 is a diagram showing a configuration of the correction optical system 41 incorporated in the optical element inspection apparatus 51 of FIG. The correction optical system 41 includes a cemented spherical lens 42 and cylindrical surface lenses 43 and 44. Since the outgoing wavefront from the test optical element 40 has a rotationally asymmetric shape, the correction optical system 41 includes optical elements 43 and 44 having rotationally asymmetric optical surfaces. By arranging such a correction optical system 41 behind the test optical element 40, the wavefront emitted from the test optical element 40 can be converted into a substantially plane wave, and the fringe density of interference fringes observed by the CCD 30 Becomes low and becomes an interference fringe that can be analyzed.

  FIG. 10 is a diagram illustrating an example of a simulation result of interference fringes generated when the test optical element 40 and the correction optical system 41 are incorporated in the optical element inspection apparatus 51. Thus, by converting the outgoing wavefront from the test optical element 40 into a substantially plane wave by the correction optical system 41, an interference fringe having a low fringe density and analyzable is generated. Note that the pass / fail judgment method for the optical element to be tested is the same as in the first embodiment.

  FIG. 11 shows an enlarged view of the test optical element 40 in FIG. 9 and its periphery. Hereinafter, the installation position of the optical element 40 to be tested in the optical element inspection apparatus 51 will be described with reference to FIG. The test optical element 40 is installed so that the optical axis of the light beam incident on the test optical element 40 coincides with the central axis of the surface (r-plane in FIG. 11) corresponding to the diaphragm surface of the imaging optical system. Further, the test optical element 40 is installed so that the optical axis of the light beam emitted from the test optical element 40 coincides with the central axis of the surface corresponding to the imaging surface of the imaging optical system (s-plane in FIG. 11). . By installing the test optical element 40 in this way, the central axis of the correction optical system 41 arranged as in numerical data described later and the optical axis of the light beam emitted from the test optical element 40 are matched. The interference fringes as shown in FIG. 10 can be generated.

  Table 3 below shows numerical data of the optical members constituting the condenser lens 39, the test optical element 40, and the correction optical system 41 shown in FIG. The test optical element 40 in FIG. 8 is equivalent to the test optical element 40 included in the imaging optical system 48 in FIG.

  In the numerical data in Table 3, “CYL” indicates a cylindrical optical surface. The cylindrical optical surface is an optical surface having a different curvature radius in the Y direction and a curvature radius in the X direction. Numerical data is shown with the respective curvature radii being “RDY” and “RDX”. In the following numerical data, the optical surface of the optical element 40 to be tested is omitted. The optical surface of the test optical element 40 is described in the numerical data of the imaging optical system 48 in Table 1 above. The f-plane to h-plane and i-plane to o-plane correspond to the converging lens 39 and the optical surface of the correction optical system 41 shown in FIG. Corresponds to the imaging surface of the imaging optical system of the imaging optical system of FIG.

[Table 3]
Surface number Curvature radius Surface spacing Refractive index (d-line) Abbe number (d-line)
1 (F side) 27.97 9.50 1.6667 48.3
2 (g-plane) -18.85 2.50 1.7283 28.5
3 (h surface) -152.94 40.00
4 (r-plane) ∞
(Test optical element 40: Table 1 shows numerical data)
5 (s-plane) ∞ 22.90
6 (i-plane) 118.66 3.00 1.7283 28.3
7 (j-plane) 16.08 11.04 1.6700 47.2
8 (k surface) -21.17 100.00
9 (1 side) CYL [1] 3.30 1.5163 64.1
10 (m-plane) ∞ 92.00
11 (n-plane) ∞ 4.00 1.5163 64.1
12 (o side) CYL [2]
RDY RDX
CYL [1] -67.47 ∞
CYL [2] -129.75 ∞
.

  In the above-described embodiment, the correction optical systems 23, 35, and 41 are described as being disposed on the transmitted wavefront side (outgoing light side) of the test optical elements 22, 34, and 40, but the test optical element 22 is described. , 34 and 40 can be provided on the incident light side to obtain the same operation and effect.

It is a figure which shows the structure of the optical element inspection apparatus of Example 1 of this invention. It is a flowchart which shows the acceptance / rejection determination procedure of a test optical element. It is a figure which shows the structure of the optical element inspection apparatus of Example 2 of this invention. It is a figure which shows a mode that the light beam passes in the imaging optical system using the test optical element of Example 2 and Example 3. FIG. It is a figure which shows the structure of the correction | amendment optical system incorporated in the optical element inspection apparatus of FIG. It is a figure which shows one example of the simulation result of the interference fringe produced | generated with the optical element inspection apparatus of Example 2. FIG. It is the figure which expanded the to-be-tested optical element of FIG. 5, and its periphery. It is a figure which shows the structure of the optical element inspection apparatus of Example 3 of this invention. It is a figure which shows the structure of the correction | amendment optical system incorporated in the optical element inspection apparatus of FIG. It is a figure which shows one example of the simulation result of the interference fringe produced | generated with the optical element inspection apparatus of Example 3. FIG. It is the figure which expanded the to-be-tested optical element of FIG. 9, and its periphery.

Explanation of symbols

R ... Reference beam M ... Test beam 11 ... Laser light source 12 ... Variable ND filter 13 ... Polarizing plate 14 ... Objective lens 15 ... Pinhole 16 ... Spatial filter 17 ... Collimator lens 18 ... Beam splitting means 19 ... Beam expander 20 ... Reference beam reflecting member 21 ... Test beam reflecting member 22 ... Test optical element 23 ... Correction optical system 24, 25 ... Spherical lens 26 ... Flux combining means 27 ... Field stop 28 ... Imaging means 29 ... Zoom lens 30 ... CCD
DESCRIPTION OF SYMBOLS 31 ... Interference fringe analyzer 32 ... Input device 33 ... Output device 34 ... Test optical element 35 ... Correction optical system 36 ... Joint spherical lens 37 ... Cylindrical surface lens 39 ... Condensing lens 40 ... Test optical element 41 ... Correction optics System 42: Spherical spherical lens 43, 44 ... Cylindrical lens 45, 46 ... Cover glass 47 ... Imaging surface 48 ... Imaging optical system 51 ... Optical element inspection device (present invention)

Claims (4)

A light source, a light beam splitting means for splitting a light beam from the light source into a test light beam and a reference light beam, and a test light element arranged in a test light beam in which the test optical element is arranged, and transmitted through the test optical element based on a design value A correction optical system that converts a wavefront into a substantially flat surface, and a light beam combining unit that combines the test light beam that has passed through the correction optical system and the reference light beam that has been converted into a parallel light beam through an optical path different from the test light beam, Imaging means for imaging the light beam transmitted through the light beam combining means, parameter calculation means for calculating a parameter relating to a wavefront transmitted through the optical element to be measured based on interference fringes formed by the imaging means, and An optical element inspection apparatus comprising: an evaluation value calculation unit that calculates an evaluation value of the optical element to be tested based on the evaluation value. Arranged in the test light beam in which the light source, the light beam splitting means for splitting the light beam from the light source into the test light beam and the reference light beam, at least one reflecting means for deflecting the test light beam, and the test optical element are arranged A correction optical system that converts the transmitted wavefront of the test optical element based on a design value into a substantially flat surface, and the test light beam that has passed through the correction optical system and the test light beam are converted into parallel light beams through different optical paths. A light beam combining unit that combines the reference light beam, an imaging unit that images the light beam that has passed through the beam combining unit, and an arithmetic unit that determines whether the optical element to be tested is acceptable or not from the interference fringes formed by the imaging unit. An optical element inspection apparatus comprising: at least one of the reflecting means for deflecting a test light beam is a reflection surface of the test optical element. The optical element inspection apparatus according to claim 1, wherein the correction optical system has at least one rotationally symmetric optical surface and at least one rotationally asymmetric optical surface. The evaluation value calculating means compares the parameter relating to the transmitted wavefront of the optical element to be measured calculated using the design value of the optical element to be measured with the parameter from the parameter calculating means, thereby The optical element inspection apparatus according to claim 1, wherein an evaluation value of the optical analysis element is calculated.

Images